Add WASM support

[notgull]

Maybe we could get the functions to fire once document.onload is called?

[stan-stately]

Just use wasm_bindgen(start)

#[cfg_attr(not(target_family = "wasm"), ctor::ctor)]
#[cfg_attr(target_family = "wasm", wasm_bindgen(start))]
fn init() {
    // ...
}

[mmastrac]

I can try implementing this, but I don't have a good toolchain setup to test.